Method and apparatus for detecting a compatible phantom powered device using common mode signaling

ABSTRACT

A method and an apparatus provide for determining whether a data terminal equipment (DTE) device represents a compatible device lacking an independent power supply and adapted to be powered using phantom power over a wired connection from a communications device such as a switch. A detection signal may be transmitted from the communications device to an identity network connected to the DTE. A response detection signal may be returned and checked in a receiver at the communications device. A switch may then be closed to provide phantom power if the result of the check indicates that the DTE is a compatible device adapted to receive phantom power. Compatible DTE device may include telephones, Voice over IP (VoIP, IP or Ethernet) telephones, network access devices, computers, and the like.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for detectingthe presence of a connected device of a particular class, such as atelephone that may require phantom power to be supplied over twistedpair wiring.

BACKGROUND OF THE INVENTION

Telephones and other types of data terminal equipment (DTE) areroutinely used for voice data and other forms of telecommunication.Examples of these include voice communication devices or telephonesoperating through a private branch exchange (PBX) or key telephonesystem. PBX-type and key telephone system-type telephones typicallyrequire the application of external electrical power in order tooperate. The power is used to energize circuits within the telephonecircuitry, such as processing displays, etc.

There are essentially two practical methods available for powering suchtelephones. The first method provides power directly to the telephone.This may be accomplished by a wall-mounted transformer providing adirect current (DC) or alternating current (AC) low voltage power supplyto the telephone from the electric power grid. Such direct power methodshave a number of drawbacks. Apart from continuous occupation of apotentially scarce electrical outlet, during a power grid disruption,the power to the telephone may be disconnected rendering the telephoneinoperative and effectively precluding emergency telephone usage duringthe black out.

The second method for providing telephone power involves supplyingso-called “phantom power” by coupling a power signal (typically up toabout 48 volts DC) to the telephone over twisted pair lines as taught,for example, in U.S. Pat. No. 6,115,468 entitled “Power Feed forEthernet Telephones via Ethernet Link”. In accordance with a specificembodiment of the aforementioned patent, as illustrated in FIG. 1hereof, a system 10 including a plurality of data ports 12, 14 and 16within a communication device such as a switch 18 is provided totransmit data on lines 20 and 22, 24 and 26, and 28 and 30 to and fromfirst, second and third load devices 32, 34 and 36, respectively. Loaddevices 32, 34 and 36 may be associated with Ethernet telephones and/orother Ethernet devices 38, 40 and 42 respectively, requiring power to betransmitted to them in addition to data over Ethernet twisted pairlines.

Turning to the first port 12 in FIG. 1 as an example, data on lines 22and 20 are provided to transmitter 44 and from receiver 46,respectively. Transmitter 44 drives data traffic along pair 48, whilereceiver 46 receives data from pair 50. First transformer 52 includes afirst primary 54 connected to pair 48, and a second primary 56 connectedto pair 50.

A similar arrangement exists at first load 32. Second transformer 58includes a first secondary 60 and a second secondary 62. These arerespectively connected to pairs 64 and 66 that are, respectively,connected through receiver 68 and transmitter 70 to load device 32.Ethernet link 72 couples first and second secondaries 74 and 76 of firsttransformer 52 to first and second primaries 78 and 80 of secondtransformer 58. Ethernet link 72 preferably comprises a pair of twistedpair conductors 82 a and 82 b, wherein twisted pair 82 a connects firstsecondary 74 to first primary 78 and twisted pair 82 b connects secondsecondary 76 to second primary 80.

Power coupling may be provided as follows: Secondaries 74 and 76 offirst transformer 52 each include a center tap 84 and 86 respectively.Center tap 84 connects to the positive lead 88 of a power supply 90, andcenter tap 86 connects to the negative lead 92 of power supply 90, whichmay, preferably, include an uninterruptible power supply (UPS). DCfiltering components 94 a, 94 b and 94 c may be provided as well knownto those of ordinary skill in the art. Now the entire loop of twistedpair 82 a is at the potential of positive lead 88 while the entire loopof twisted pair 82 b is at the potential of negative lead 92 without anyimpact on data transmission. A power processor 96 may preferably beattached to center taps 98 and 100 of first and second primaries 80 and82 of second transformer 58, respectively, so as to provide a DC powersource to the power processor 96.

The power processor 96, shown in more detail in FIG. 2, conventionallyincludes a filter 102, a rectifier 104, a filter capacitor 106 and aDC-DC converter 108. Other similar arrangements are also well known tothose of ordinary skill in the art. The power processor 96 may performDC-DC power conversion and filtering required, as well as provide powerover leads 110 and 112 to load 32, which may be an Ethernet telephone orother device.

Returning to FIG. 1, the communication system 10 may be divided into aswitch 18 and DTE devices 38, 40 and 42. The switch 18 may be foundwithin a telephone equipment room, for example. Cables may then berouted from the load devices 32, 34 and 36 to the switch 18 forconnecting to conventional jacks or connectors of the switch (not shown)such as the well-known type RJ-45 connectors (as used herein the termRJ-45 type connector is intended to include both make (plugs) and female(sockets) variants thereof). Because the switch 18 supplies a DC bias tothe center taps 84 and 86, and because the switch 18 may conceivably beused with legacy DTE potentially not compatible with the application ofsuch a voltage, it would be desirable to provide a mechanism fordetecting which ports of such a switch 18, should and should not havephantom power applied. Phantom power should then be supplied to a DTE ifthe switch establishes that the DTE is a compatible IP telephone orother compatible powerable network device. However, a prioridetermination of this condition is not presently available, and thus arequirement for power at the DTE cannot presently be determined.Accordingly, there exists a need for an efficient, simple andinexpensive method and apparatus for detection of a compatible IP devicethat should be provided with phantom power.

SUMMARY OF THE INVENTION

A method and an apparatus provide for determining whether a dataterminal equipment (DTE) device represents a compatible device lackingan independent power supply and adapted to be powered using phantompower over a wired connection from a communications device such as aswitch. A detection signal may be transmitted from the communicationsdevice to an identity network connected to the DTE. A response detectionsignal may be returned and checked in a receiver at the communicationsdevice. A switch may then be closed to provide phantom power if theresult of the check indicates that the DTE is a compatible deviceadapted to receive phantom power. Compatible DTE devices may includetelephones, Voice over IP (VoIP, or IP or Ethernet) telephones, networkaccess devices, computers and the like.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated into and constitute apart of this specification illustrate one or more embodiments of theinvention and, together with the present description, serve to explainthe principles and implementations of the invention.

In the drawings:

FIG. 1 is an electrical schematic diagram of a phantom powerdistribution system for an Ethernet telephones in accordance with theprior art.

FIG. 2 is an electrical schematic diagram of a prior art telephonephantom power extraction system in accordance with the prior art.

FIG. 3 is an electrical schematic diagram illustrating a phantompowerable DTE detection system in accordance with a specific embodimentof the present invention.

FIGS. 4A, 4B, 4C, 4D, 4E and 4F are electrical schematic diagrams ofseveral variants of an identity network in accordance with specificembodiments of the present invention.

FIGS. 5 and 6 are amplitude versus time graphs illustrating detectionsignals and response signals in accordance with specific embodiments ofthe present invention.

FIG. 7 is a process flow diagram illustrating a method of compatible DTEdevice detection and phantom power provision in accordance with aspecific embodiment of the present invention.

FIG. 8 is a system block diagram of a portion of a compatible DTE devicedetection and phantom power provision system in accordance with anotherspecific embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention are described herein in the contextof a method and apparatus for detecting a compatible phantom powereddevice using common mode signaling. Those of ordinary skill in the artwill realize that the following description of the present invention isillustrative only and not in any way limiting. Other embodiments of theinvention will readily suggest themselves to such skilled persons havingthe benefits of this disclosure. Reference will now be made in detail toan implementation of the present invention as illustrated in theaccompanying drawings. The same reference numbers will be usedthroughout the drawings and the following description to refer to thesame or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are described. It will of course beappreciated that in the development of any such actual implementation,numerous implementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system- andbusiness-related constraints, and that these goals will vary from oneimplementation to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

In accordance with the present invention, the components, process steps,and/or data structures may be implemented using various types ofoperating systems, computing platforms, computer programs, and/orgeneral purpose machines. In addition, those of ordinary skill in theart will readily recognize that devices of a less general purposenature, such as hardwired devices, or the like, may also be used withoutdeparting from the scope and spirit of the inventive concepts disclosedherein.

The present invention relates to a method and apparatus to determinewhether a DTE device requires phantom electrical power to be suppliedvia center taps in magnetic transformers as illustrated in FIG. 1. Theapparatus transmits a detection signal to ascertain the presence of aDTE device requiring phantom power and analyzes the response signal tomake the determination. The apparatus includes switches or similardevices to both connect direct current for remote phantom powertransmission and to disable detection signal interference during dataexchange. The method includes a sequence of operations with a logic gateto open or close the switches in accordance with the received responsesignal. The switches may be electromechanical, or more preferably,electronic (e.g., transistors and MOSFETs).

Electric current is carried across a transformer from primary tosecondary windings by differential mode (opposite polarity signaling).In common mode (same polarity signaling), an AC signal connected to atransmit transformer center tap may be propagated to a receivetransformer center tap without echoing a ghost signal across eithertransformer. This ghost signal blockage results from the common modedestructive interference (signal amplitudes at 180° phase difference) inthe transformer core, and by using a well-controlled signal having alimited bandwidth. Similarly, a DC signal will normally be blocked incommon mode signaling from the primary to the secondary, but may beapplied to the center tap and propagated as illustrated in FIG. 1.

FIG. 3 illustrates an electric schematic diagram for the DTE-detectingcommunication device 114 (such as an Ethernet, telephone or VoIP switch)and the phantom powerable DTE device 1 16 connected by wires or cables118. The communication device 114 may include a PHY (physical layerdevice) 120, while the DTE device 116 may include a terminal device 122.A signal generator 124 and a signal analyzer 126 may be used,respectively, to send and receive a common mode detection signal 128 forquerying whether a data connection is to be established and/or power isto be applied. The detection signal 128 may be represented by asinusoidal pulse and is input to an isolator 130 (for surge protection)and then into a primary winding 132 of a first transformer 134terminating at termination network 136. Then detection signal 128 ispreferably a portion of a sinusoidal waveform as illustrated but thoseof ordinary skill in the art will now realize that other signals mayalso be propagated.

The detection signal 128 is carried across the first transformer 134through a secondary winding 138 to a source transmitter 140 having asecond transformer 142. The detection signal 128 is input to a centertap 144 of transformer 142 and passes simultaneously through portions146 a and 146 b of secondary winding 146 of transformers 142. The centertap 144 may also be connected to a termination network 148 (includingresistor, capacitor and/or ground) for providing a common modetermination. The detection signal 128 then passes out from sourcetransmitter 140 across conductors 150 a and 150 b to a connector block152 a, of communication device 114 over wires 118 a and 118 b of cable118 to a connector block 152 b of a DTE receiver 154 of DTE device 116having a third transformer 156.

The detection signal 128 passes simultaneously through portions 158 aand 158 b of primary winding 158 of third transformer 156 to center tap160 of transformer 156, and then in parallel through (1) an identitynetwork 162 and (2) a control network that includes a power switch 164and a power processor 96 for processing phantom power to power DTEdevice 116. In accordance with one specific embodiment of the presentinvention, power switch 164 is a three terminal device having a signalinput 166, a signal output 168 and a control input 170. In accordancewith this specific embodiment, DC phantom power is provided over lines118 a, 118 b to center tap 160 once a phantom powerable device isdetected. Accordingly, by coupling control input 170 to signal input 166power switch 164 will latch closed while phantom power is available.Those of ordinary skill in the art will now realize that a plethora ofother ways exist to achieve the same result. Thus, the power switch 164is preferably defaulted to open in the absence of power to allow thedetection signal 128 to pass through the identity network 162. Identitynetwork 162 is preferably designed to interact with detection signal 128in such a way that signal analyzer 126 can readily distinguish whenidentity network 162 is present (i.e., in a compatible phantom powerabledevice) and when it is absent (i.e., in a legacy device). Identitynetwork 162 should also preferably be designed so as not to interferewith the operation of power processor 96 when switch 164 is closed. Thusidentity network 162 can either be adopted to switch out of the circuitcontemporaneously with the application of phantom power, or identitynetwork 162 can include a circuit which need not be switched out such asa capacitor C1 (FIG. 4A) or a relatively high valued resistor R1 (FIG.4B) or the like.

Identity network 162 (FIG. 4C) could even include, as will now beapparent to those of ordinary skill in the art, a capacitor C2 to powera memory and a nonvolatile serial memory device M1, so as to read out aseries of pulses specifically identifying the type and requirements ofthe DTE 116. The capacitor C2 could be charged, for example, by a seriesof detection signal pulses and a rectifier D1 and when sufficientvoltage is achieved in C2, a send signal will initiate a memory readoutfrom memory M1. As shown in FIG. 4D, the identity network 162 mayalternatively include an inductor L1 to induce a temporal shift to thedetection signal which could then be detected by signal analyzer 126(which would them be supplied with a signal indicating the departuretime of detection signal 128 so that it could measure the round triptime looking for a “correct” round trip time in order to provide phantompower). FIG. 4E illustrates a diode used as the identity network. Thediode rectifies a sine wave input which would easily be detected at thesignal analyzer 126. FIG. 4F illustrates a zener diode as the identitynetwork. The zener diode limits the voltage passing through it inaddition to rectifying an input signal. This is also easily detected atsignal analyzer 126 and well within the capabilities of those ofordinary skill in the art. Identity network 162 is therefore designed toallow the passage of the detection signal 128 (or a variant thereof) tothe DTE transmitter 172 causing the signal to be returned and recognizedby signal analyzer 126. If the DTE device 116 is a conventional networkdevice not requiring phantom power, the identity network 162 will likelynot be present, the detection signal will probably not loop back, or ifit does, it will lack the characteristics that the signal analyzer 126is looking for that are to be imparted by the identity network, andphantom power will therefore not be applied to the part corresponding toDTE device 116.

The (possibly modified) detection signal 128 enters DTE transmitter 172having a fourth transformer 174. The detection signal 128 enterstransformer 174 through center tap 176 and passes through secondarywinding portions 178 a and 178 b of secondary winding 178 back towardsthe communications device 114 over conductors 180 a and 180 b across theconnector blocks 152 b, cable 118 and connector block 152 a and into thesource receiver 182. A fifth transformer 184 may include secondarywinding portions 186 a, 186 b of secondary winding 186 through which thedetection signal 128 passes, before exiting through source receivercenter tap 188 and into a postconditioner 190. The center tap 188 may beconnected to a termination network 192. A sixth transformer 194 in thepostconditioner 190 passes the detection signal 128 through a primarywinding 196 (rather than through a center tap) transferring thedetection signal 128 to a secondary winding 198 and into signal analyzer126, and a termination network 200 providing isolation and protectionfor the active circuitry of the receiver. The analyzer 126 may serve tocheck received response signal characteristics due to the application ofthe detection signal 128 to the identity network 162 and determine ifphantom power should be applied.

If the signal analyzer 126 determines that phantom power should beapplied, a control signal on line 202 is generated to command switch 204to close thereby providing power from power supply 90 through switch 204to center taps 144 and 168 in a manner similar to that discussed in U.S.Pat. No. 6,115,468 discussed in detail above.

The power switch 164 may remain open if, despite a received return ofdetection signal 128, a data signal is also communicated from the DTEdevice 116. Such a condition indicates that the DTE device 116 alreadyhas access to an independent power source and does not require phantompower. An indication of this condition may be passed, for example, fromPHY 120 over line 206 to signal analyzer 126 so that signal analyzer 126withholds a signal on line 202 where data is detected from PHY 120 evenif the signal 128 received at signal analyzer 126 over line 208 wouldotherwise indicate that phantom power should be applied.

Transmitted and received sinusoidal pulses are shown in FIG. 5 torepresent an example form for a detection signal 128. A transmittedpulse 210 for a half-wavelength duration can be described by peakamplitude 212, start time 214, end time 216 and pulse duration 218therebetween. A received pulse 220 can be described by peak amplitude222, start time 224, end time 226 and pulse duration 228 therebetween.The received pulse 220 may be detectable provided its peak amplitude 222reaches a detection threshold 230. In accordance with a specificembodiment of the invention, the pulse form exhibits a single frequencysinusoidal pattern, although other waveform shapes are possible as thoseof ordinary skill in the art will now recognize.

Due to resistance in the conductors the received pulse may be attenuatedso that received amplitude 222 is attenuated from the transmittedamplitude 212 by a difference 232. Due to line impedance, the receivedpulse may be delayed so that the received start time 224 may lag thetransmitted start time 214 by a delay 234. In addition, the receivedpulse may spread so that its duration 228 may be longer than thetransmitted duration 218 by the difference between durations 228 and218. The magnitude of the amplitude difference may be used to enable theanalyzer 126 to distinguish a DTE device requiring phantom power from aDTE device not requiring phantom power. In particular, a return signalwith an amplitude in the noise level, e.g., below threshold 230, mayindicate a device with no need for phantom power. A return signal with arelatively unattenuated amplitude may indicate a DTE device with a needfor phantom power.

In accordance with a specific embodiment of the present invention, e.g.,the use of an identity network 162 as shown in FIG. 4A, in order toavoid saturating the DTE identity network 162, the time between pulses210 should preferably be sufficient to enable charge dissipation of theidentity network 162 where it contains capacitive or inductive element.FIG. 6 shows two transmission pulses having peaks 236 and 238 with aperiod 240 therebetween. The period 240 may be much longer than thepulse duration 218. The transmission pulse duration 218 may last in thenanosecond or microsecond range, while the period 230 may endure intoseveral milliseconds.

A communications device in accordance with the present invention mayencounter three scenarios: (1) no response signal, (2) a proper responsesignal coupled with active data transmission, and (3) a proper responsesignal coupled with no active data transmission indicating a need forphantom power.

FIG. 7 is a flow chart 242 illustrating a method used to determinewhether or not to apply phantom power to an Ethernet circuit inaccordance with a specific embodiment of the present invention.

The communications device 114 transmits a detection signal 128 at block244 and evaluates the response with signal analyzer 126 at block 246. Ifno signal is detected, control returns to block 244 and thecommunications device 114 continues to look for a device requiringphantom power. If a signal is detected, control optionally passes toblock 248 where it is determined whether a data signal has been receivedfrom the PHY 120. If a data signal has been received then there is noneed to take further action because this result means that the DTEdevice is operating and obviously has a power source. Control maytransfer to block 254 as discussed below.

If no data signal is detected at block 248, then control transfers toblock 250 where the signal analyzer analyzes the response signal for acharacteristic indicating that it is a DTE device (such as a compatibleIP telephone), which requires phantom power. If the analysis at block250 concludes that a compatible DTE device requiring phantom power isattached, control transfers to block 252 so that switches 204 and 164are closed to provide phantom power to the DTE device. While theseswitches are closed, there is no need to continue transmission ofdetection signal 128 and this is terminated at block 254. Data exchangeis initiated at block 256.

Control then transfers to block 258 where the system waits fortermination of communication (for example, DTE device is unplugged). Ifthis occurs, control transfers to block 260 and the power switches 204and 164 are opened before transfer back to block 244.

If the analysis at block 250 concludes that an incompatible device or adevice not requiring phantom power is attached, control skips block 252and goes to block 254.

Turning now to FIG. 8, another specific embodiment of the presentinvention is shown in block diagram form. In accordance with theembodiment of FIG. 8 central processing unit (CPU) 242 implementing aprogram of instructions in computer readable memory storage device 244controls the operation of signal generator 124, signal analyzer 126, andswitch 204 while optionally receiving information from PHY 120 (thepresence of data exchange with DTE device 116) and controlling switch204 with it as link 206 does in the embodiment described above. Theprecise configuration of such a computer-controlled system is wellwithin the skill of those of ordinary skill in the art and thereforeneed not be described in more detail herein.

The operation of signal analyzer 126 depends entirely on the nature ofthe identity network 162 chosen. In a very simple embodiment, identitynetwork 162 may be a capacitor. In this case, the pulse will passthrough identity network somewhat changed but identity network 162 willnot interfere with the phantom power processor at DTE device 116. Sincethe response signal comes back, the signal analyzer can conclude thatthe DTE device 116 is compatible. More sophisticated approaches can beused, such as to more specifically identify the DTE device 116 and applya particular voltage signal selected from among, a plurality of voltagesignals available, and the like. Different resistances, inductances orserial memory contents could, for example, be used to provide such moredetailed information.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this application that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.The invention, therefore, is not to be restricted except in the spiritof the appended claims.

What is claimed is:
 1. A data terminal equipment (DTE) devicecomprising: a port having a plurality of electrical conductors forcommunicating with a communications device; a first transformer windingcoupled to a first pair of said plurality of electrical conductors and afirst center tap disposed in said first transformer winding; a secondtransformer winding coupled to a second pair of said plurality ofelectrical conductors and a second center tap disposed in said secondtransformer winding; a power processor having a first and second inputfor receiving phantom power and a first and second output for providingelectrical power to the DTE device; a switch controlled by a signal onsaid first pair of said electrical conductors, said switch having aswitch input coupled to said first center tap and a switch outputcoupled to said first input of said power processor, said second inputof said power processor coupled to said second center tap; and anidentity network coupled between said first center tap and said secondcenter tap.
 2. An apparatus in accordance with claim 1 wherein saididentity network comprises a capacitor.
 3. An apparatus in accordancewith claim 1 wherein said identity network comprises a resistor.
 4. Anapparatus in accordance with claim 1 wherein said identity networkcomprises an inductor.
 5. An apparatus in accordance with claim 1wherein said identity network comprises a diode.
 6. An apparatus inaccordance with claim 5, wherein said identity network comprises a zenerdiode.
 7. An apparatus in accordance with claim 1 wherein said identitynetwork comprises a serial memory device having data stored therein. 8.An apparatus in accordance with claim 1, wherein said switch includes acontrol input and said control input is coupled to said switch input. 9.An apparatus in accordance with claim 1 wherein said port includes anRJ-45 type connector.
 10. A method for providing a compatiblecommunications device with a signal indicating that phantom power shouldbe supplied to a connected data terminal equipment (DTE) device, saidmethod comprising: receiving a detection signal over a first pair ofconductors; coupling said first pair of conductors across a firsttransformer winding, said first transformer winding including a firstcenter tap; extracting a signal at said first center tap; coupling anidentity network between said first center tap and a second center tapof a second transformer winding; generating a response signal byapplying said extracted signal to an input of said identity network; andtransmitting said response signal over a second pair of conductors byapplying an output of said identity network to said second center tapand coupling said second pair of conductors across said secondtransformer winding, said second center tap being a center tap of saidsecond transformer winding.
 11. A method in accordance with claim 10,further comprising: receiving phantom power between said first centertap and said second center tap.
 12. A method in accordance with claim11, further comprising: applying said phantom power to a powerprocessor.
 13. A method in accordance with claim 12, wherein: thephantom power is applied to the power processor through a switchresponsive to the presence of phantom power between said first andsecond center taps.
 14. An apparatus for providing a compatiblecommunications device with a signal indicating that phantom power shouldbe supplied to a connected data terminal equipment (DTE) device, saidapparatus comprising: means for receiving a detection signal over afirst pair of conductors; means for coupling said first pair ofconductors across a first transformer winding, said first transformerwinding including a first center tap; means for extracting a signal atsaid first center tap; means for coupling an identity network betweensaid first center tap and a second center tap of a second transformerwinding; means for generating a response signal by applying saidextracted signal to an input of said identity network; and means fortransmitting said response signal over a second pair of conductors byapplying an output of said identity network to said second center tapand coupling said second pair of conductors across said secondtransformer winding, said second center tap being a center tap of saidsecond transformer winding first winding of said second transformer. 15.An apparatus in accordance with claim 14, further comprising: means forreceiving phantom power between said first center tap and said secondcenter tap.
 16. An apparatus in accordance with claim 15, furthercomprising: means for applying said phantom power to a power processor.17. An apparatus in accordance with claim 16, wherein: the phantom poweris applied to the power processor through a switch responsive to thepresence of phantom power between said first and second center taps.